1. Field of the Invention
The present invention is for an intraocular lens, and more particularly, pertains to a small corneal implant lens which provides multifocal capability for the correction of presbyopia or ametropia and is coated with a hydrogel material for improved transmission of nutrients and reduced irritation of the tissue surrounding the implant.
The invention relates specifically to a corneal implant lens which is substantially smaller than the pupil and is coated with a hydrogel material. In the preferred form, the lens is annular in shape and the central hole is filled with a hydrogel material. The inner and outer circumferences have anti-glare edges. The outer edge is covered with a hydrogel material which serves to increase the physical diameter of the lens to improve the fixation characteristics by reducing the irritation normally caused by edges and to reduce the tendency of an otherwise small lens to be displaced by casual rubbing of the eye by the user.
2. Description of the Prior Art
Various annular corneal implant lens designs exist in the prior art. Some configurations have two or more discrete lens areas which serve to bring the impinging rays from an object to a sharp focus on a portion of the retina serviced by the lens area having a focal length closest to the optimum for the object distance. The use of smaller corneal implant lenses has also been suggested in the prior art.
While corneal implant lenses have been found to offer significant advantages over other methods of correcting certain vision defects, the implants introduce their own set of problems. For example, the cornea is living tissue and must continue to receive nutrients. This has led to the development of lenses with holes to accommodate the passage of nutrient carrying liquids. It has also led to the investigation of smaller lenses, which, because of their small size, offer less of an impediment to the transfer of liquids than other, larger lenses. While reducing the size of the lens provides an advantageous improvement in the nutrient flow, the smaller lenses are more likely to be displaced from their initial implant position by such actions as the patient rubbing the eyes containing the lens. The lamellae of the corneal tissue are oriented in planes which are generally parallel to the surface. Since the corneal implant lens is oriented in the same plane, there is little impediment to movement along the plane, between the lamellae layers. The unconscious nature of rubbing the eye makes it virtually impossible to prevent the wearer from occasionally touching the eye and potentially displacing the lens. Fixation techniques used with lenses positioned in the capsular bag of a removed natural lens are not applicable to corneal implants.
The existing devices and surgical implant techniques do not provide a satisfactory solution to the fixation problem. This is one of the reasons that the small corneal implant lenses have not found wide use.
Another problem, also related to the physical anatomical structure of the corneal lamellae, is the irritation caused by the edges of the implant lens. It is unfortunate that the edge geometry which causes the least irritation generates annoying secondary images due to diffraction and reflection. The edge geometry which has been found to substantially reduce secondary images is unacceptable from the standpoint of tissue irritation and the attendant complications that such irritation causes.
Of course, there is the need for a multifocal lens which can correct for the loss of accommodation which accompanies aging. One technique is to form the lens with a centrally positioned hole, which has no correction, allowing the eye to focus two images on the retina. While this technique provides substantial advantages, the interior edge generates further unwanted secondary images by diffraction and reflection.
What is needed is a small corneal implant lens which does not provide a substantial impediment to the natural flow of nutrients in the cornea but is nevertheless not prone to accidental displacement by casual rubbing of the eye, which does not irritate the corneal tissue and does not have secondary images caused by edge diffraction. Even further, the lens should provide multifocal capability. Quite unfortunately, the requirements for nutrient flow are such that they contradict the requirements for good fixation, while the larger lenses that provide better fixation do not allow adequate nutrient flow. Similarly, the reduction of edge diffraction effects has been accomplished at the expense of increased tissue irritation. Or, conversely, the reduction of tissue irritation has been achieved with techniques that increase the secondary image problem.
The multifocal corneal implant lens of this invention is quite small in size, but, because of the hydrogel extension about the periphery, is not easily displaced by casual rubbing of the eye. Holes in the lens which allow the passage of nutrients are filled with hydrogel which allows the flow of nutrients but prevents the hole from being filled with scar tissue. The hydrogel coating significantly improves the compatibility of the lens to the living tissue of the cornea and also serves to reduce the irritation otherwise caused by non-glare edges of the lens. The effectiveness of the non-glare edges is further improved by the hydrogel coating, which has an index of refraction intermediate between the lens and the tissue of the cornea.